1. Field of the Invention
The present invention relates to imprint lithography templates. More particularly, to imprint lithography templates for use in micro- and nano-imprint lithography processes.
2. Description of the Relevant Art
Optical lithography techniques are currently used to make most microelectronic devices. However, it is believed that these methods are reaching their limits in resolution. Sub-micron scale lithography has been a critical process in the microelectronics industry. The use of sub-micron scale lithography allows manufacturers to meet the increased demand for smaller and more densely packed electronic components on chips. It is expected that in the coming years, the microelectronics industry will pursue structures that are smaller than about 50 nm. Further, there are emerging applications of nanometer scale lithography in the areas of opto-electronics and magnetic storage. For example, photonic crystals and high-density patterned magnetic memory of the order of terabytes per square inch require nanometer scale lithography.
For making sub-50 nm structures, optical lithography techniques may require the use of very short wavelengths of light (e.g., about 13.2 nm). At these short wavelengths, many common materials may not be optically transparent and therefore imaging systems typically have to be constructed using complicated reflective optics. Furthermore, obtaining a light source that has sufficient output intensity at these wavelengths may be difficult. Such systems may lead to extremely complicated equipment and processes that may be prohibitively expensive. It is believed that high-resolution e-beam lithography techniques, though very precise, may be too slow for high-volume commercial applications.
Imprint lithography processes have demonstrated the ability to replicate high-resolution (sub-50 nm) images on substrates using templates that contain images as topography on their surfaces. It is believed that imprint lithography may be an alternative to optical lithography for use in patterning substrates in the manufacture of microelectronic devices, optical devices, MEMS, opto-electronics, patterned magnetic media for storage applications, etc. Imprint lithography techniques may be superior to optical lithography for making three-dimensional structures such as micro lenses and T-gate structures.
For production-scale imprint lithography, it may be desirable to place patterned regions as close as possible to each other without interfering with subsequent imprints. This effectively maximizes the patternable area on the substrate. In order to accomplish this goal, the location of the any excess fluid that is expelled from the patterned area should be well confined and repeatable. As such, the individual components, including the template, substrate, fluid and any other materials that may affect the physical properties of the system, including but not limited to surface energy, interfacial energies, Hamacker constants, Van der Waals"" forces, viscosity, density, opacity, etc., should be engineered properly to accommodate a repeatable process. Accordingly, a need exists for a way of controlling the spread of excess fluid outside desired patterning regions that can facilitate production-scale imprint lithography.
The embodiments described herein include imprint lithography templates, methods for forming and using imprint lithography templates, and template holders.
In an embodiment, an imprint lithography template may be substantially transparent to activating light (e.g., ultraviolet light). Such a template may include a body having a first surface. The template may further include a plurality of recesses on the first surface. In various embodiments, the first surface may be substantially planar, parabolic, or spherical. At least a portion of the recesses may have a feature size of less than about 250 nm. In some embodiments, the template may further include at least one alignment mark on the body. In some embodiments, the template may further include a gap sensing area.
In various embodiments, the body may be formed in whole, or in part of silicon, silicon dioxide, silicon germanium carbon, gallium nitride, silicon germanium, sapphire, gallium arsinide, epitaxial silicon, poly-silicon, gate oxide, quartz, indium tin oxide or combinations thereof. In some embodiments, at least a portion of the body may be formed of SiOx, where X is less than 2. For example, X may be about 1.5.
In an embodiment, the plurality of recesses on the first surface may include first recesses, having a first depth; and second recesses, having a second depth. The second depth may be greater than the first depth. For example, the first depth may be less than about 250 nm. In addition to the plurality of recesses on the first surface, the template may include at least one recess on a second surface opposite the first surface. In an embodiment, at least a portion of the recesses may have a width that varies in a direction normal to the first surface. Such recesses may be configured to accommodate changes in material properties of a light curable liquid that may be used with the template in an imprint lithography process. For example, the light curable liquid may contract or expand upon curing.
In an embodiment, a template may include an excess fluid relief structure formed in a portion of the body. For example, such a structure may be formed in a kerf area of a template.
In some embodiments, at least a portion of the first surface of the template may have a surface free energy measured at 25xc2x0 C. of less than about 40 dynes/cm. In some of these embodiments, the portion of the first surface of the template may have a surface free energy measured at 25xc2x0 C. of less than about 20 dynes/cm. For example, at least the portion of the first surface may have a surface treatment layer. The surface treatment layer may include a reaction product of an alkylsilane, a fluoroalkylsilane, or a fluoroalkyltrichlorosilane with water. For example, the surface treatment layer may include a reaction product of tridecafluoro-1,1,2,2-tetrahydrooctyl trichlorosilane with water. The surface treatment layer may reduces the surface free energy of the first surface measured at 25xc2x0 C. to less than about 40 dynes/cm, or in some cases, to less than about 20 dynes/cm.
In some embodiments, an alignment mark on the template may be substantially transparent to activating light. The alignment mark may be substantially opaque to analyzing light. In such embodiments, the analyzing light may include visible light or infrared light. The alignment mark may be formed of a material different than the material of the body. For example, the alignment mark may include SiOx where x is less than 2. For example, x may be about 1.5. Alternately, the alignment mark may include a plurality of lines etched on a surface of the body. The lines may be configured to substantially diffuse activating light, but produce an analyzable mark under analyzing light.
In some embodiments, the template may have a planarity of less than about 500 nm. In some of these embodiments, the template may have a planarity of less than about 250 nm.
In some embodiments, the template may include a conductive coating or reflective coating on at least one edge of the body. In other embodiments, the template may include a mirror coupled to at least one edge of the body.
In an embodiment, the template may include a template blank coupled to the body. For example, the body may be bonded to the template blank using a bonding agent. The template blank and the bonding agent may be substantially transparent to activating light. In some embodiments, a gap sensing area may include at least one recess having a known depth. The gap sensing area may be in the first surface or the second surface. In an embodiment, the gap sensing area may have a depth greater than about 100 nm.
In an embodiment, an imprint lithography template, as described above, may be formed by obtaining a material that is substantially transparent to activating light and forming a plurality of recesses on a first surface of the material. The method of forming the template may further include forming at least one alignment mark on the material. The plurality of recesses may be formed by etching the material. The plurality of recesses may be formed using processes including but not limited to optical lithography, electron beam lithography, ion-beam lithography, x-ray lithography, extreme ultraviolet lithography, scanning probe lithography, focused ion beam milling, interferometric lithography, epitaxial growth, thin film deposition, chemical etch, plasma etch, ion milling, or reactive ion etch. Likewise, the alignment mark may be formed using processes including but not limited to optical lithography, electron beam lithography, ion-beam lithography, x-ray lithography, extreme ultraviolet lithography, scanning probe lithography, focused ion beam milling, interferometric lithography, epitaxial growth, thin film deposition, chemical etch, plasma etch, ion milling, or reactive ion etch. For example, in some embodiments as described above, the alignment mark may include a plurality of lines formed on the template. In other embodiments, the alignment mark may be formed by depositing a second material on the material used to form the template.
A method of forming an imprint lithography template may further include shaping the material into a desired shape. For example, the material may be shaped to provide desired dimensions to the template. The desired dimensions may include a predetermined set of template dimensions. In some embodiments, the method may include coupling the material to a template blank. For example, the material may be bonded to a template blank using a bonding agent.
A surface treatment as previously described may be applied to at least a portion of the first surface of the template. In some embodiments, the surface treatment layer may be formed using a vapor-phase reaction process. For example, the material may be placed in a reaction chamber. The reaction chamber may be purged. At least one reactant chemical may be administered into the reaction chamber. It is believed that the at least one reactant chemical may react with water to form the surface treatment layer on at least a portion of the first surface. However, it is anticipated that the reactant chemical may react directly with the surface of the template, with a another chemical present on the first surface, or with itself to form the surface treatment layer.
In some embodiments, the method may also include applying a reflective coating or a conductive coating to at least one edge of the material. In other embodiments, the method may include coupling a mirror to at least one edge of the material.
To form a pattern on a substrate, a template may be placed in a template holder. The template holder may include a body, a supporting plate and at least one piezo actuator. The body may have an opening configured to receive an imprint lithography template. The body may be configured to be attached to a template support of an imprint lithography system. The supporting plate may be coupled to the body and may be substantially transparent to activating light. The supporting plate may span the opening in the body in at least one direction. The supporting plate may be formed of materials including but not limited to quartz, sapphire and SiO2. The supporting plate may be configured to inhibit deformation of a template disposed within the template holder due to forces present in an imprint lithography process. The at least one piezo actuator may be coupled to the body, and configured to alter a physical dimension of the imprint lithography template during use. For example, a piezo actuator may be configured to apply a compressive or elongating force to a template disposed within the opening. The supporting plate and/or the body may include at least one vacuum opening configured to apply vacuum to a template disposed within the opening and/or the interface of the supporting plate and the body. Additionally, a mirror or reflective coating may be applied to a surface of the body that faces inside the opening.
An imprint lithography template, as described above, may be used in a method of forming a pattern on a substrate using a patterned template. In general, a method of forming a pattern on a substrate may be accomplished by applying a light curable liquid (e.g., a photoresist material) to a substrate. An imprint lithography template is positioned above the portion of the substrate to which the light curable liquid was applied. The relative position of the template and the substrate may be adjusted such that a gap is created between the patterned template and the substrate. Activating light may be applied through the template to the liquid. Applying the activating light substantially cures the liquid. Thus, a pattern of the template is formed in the cured liquid. The template may then be separated from the cured liquid.
The method may further include determining the alignment between the patterned template and the substrate. In such a case, the substrate may include a substrate alignment mark. The template alignment mark and the substrate alignment mark may be symmetric geometric shapes. Determining the alignment of the alignment marks may include determining the centers of the substrate and template alignment marks. The locations of the centers of the alignment marks may be compared to determine alignment of the alignment marks.
In a first embodiment, the alignment between the patterned template and the substrate may be determined by applying a first wavelength of light through the patterned template. The first wavelength of light may cause the substrate alignment mark to be in focus and the template alignment mark to be out of focus with respect to an analysis tool. A second wavelength of light may then be applied through the patterned template. The second wavelength of light may cause the template alignment mark to be in focus and the substrate alignment mark to be out of focus with respect to the analysis tool. In a second embodiment, the alignment between the patterned template and the substrate may be determined by using a polarizing light alignment tool. A polarizing filter system may be placed between the polarizing light alignment tool and the template. The polarizing filter system may include a first polarizing filter substantially oriented over the substrate alignment mark and a second polarizing filter substantially oriented over the template alignment mark. The polarization of light capable of passing through the first polarization filter is substantially different then the polarization of light capable of passing through the second polarization filter. In a third embodiment, determining the alignment may be done using a moirxc3xa9 pattern detector. In a fourth embodiment, determining the alignment between the template and the substrate may include applying an analyzing light to the template. The template may include at least two materials, a first material and a second material. The alignment mark may be formed of the second material. The first and second materials may be substantially transparent to the activating light used to cure the liquid. However, the second material may produce an analyzable mark with substantial contrast when the analyzing light is applied to the template. In a fifth embodiment, the template alignment mark may include a plurality of etched lines that act as a diffraction grating toward analyzing light. Determining the alignment between the patterned template and the substrate may include applying analyzing light to the patterned template. The template alignment mark may be substantially transparent to the activating light, but may produce an analyzable mark when the analyzing light is applied to the template.
The method of forming a pattern on a substrate using a patterned template may further include adjusting the overlay placement of the patterned template and the substrate. Adjusting the overlay placement includes moving the substrate such that the template alignment mark is substantially aligned with the substrate alignment mark. For example, adjusting the overlay placement may include altering the angle of the patterned template with respect to the substrate or altering the dimensions of the patterned template. The dimensions of the template may be altered by altering the temperature of the template or applying a compressive or elongation force to the template. For example, at least one piezoelectric actuator may be coupled to the patterned template. The at least one piezoelectric actuator may alter the dimensions of the patterned template by applying a force to the template.
The activating light curable liquid may be applied to a portion of the substrate by a fluid dispenser. The liquid may be dispensed to create a predetermined pattern by moving the substrate with respect to the fluid dispenser. The predetermined pattern may be configured to inhibit the formation of air bubbles in the liquid when the template contacts the liquid. The predetermined pattern that may be also be selected such that the liquid fills the gap in an area substantially equal to the surface area of the template.
In an embodiment, positioning the patterned template and the substrate in a spaced relationship may include positioning the patterned template over the substrate and moving the patterned template toward the substrate until a desired spaced relationship is achieved. The liquid on the substrate substantially fills the gap as the patterned template is moved toward the substrate. The spaced relationship may be a distance of less than about 200 nm. In some embodiments, the patterned template and the substrate may be positioned in a substantially parallel orientation. In other embodiments, the template may be positioned over the substrate in a substantially non-parallel position. The template may be moved toward the substrate while remaining in a substantially non-parallel orientation with respect to the substrate. The template may then be oriented in a substantially parallel orientation to the substrate when the template is in a desired spaced relationship to the substrate.
In an embodiment, separating the patterned template from the cured liquid may include moving the template to a substantially non-parallel orientation and moving the patterned template away from the substrate. After separating the patterned template from the cured liquid, the cured liquid may include some features less than about 250 nm in size.
The method of forming a pattern on a substrate using a patterned template may also include determining the distance between the patterned template and the substrate. A light based measuring device may be used for this purpose. The method may include applying light to the template and the substrate. The light may include a plurality of wavelengths. Light reflected from a surface of the template and the substrate may be monitored. The distance between the template and the substrate may be determined based on the monitored light. In addition, an error signal may be generated. The error signal corresponds to the difference between a desired distance between the template and substrate and the determined distance between the template and substrate. Additionally, determinations of the distance between the template and the substrate made at 3 or more non-collinear locations may be used to determine whether the template and substrate are substantially parallel. This determination may also be used generate an error signal corresponding to a relative movement between template and the substrate required to bring them into a substantially parallel configuration.
The substrate may include but is not limited to a dielectric material, silicon, gallium, germanium, indium, quartz, sapphire, silicon dioxide, or polysilicon. The substrate may include one or more layers on the surface of the substrate. In such a case, the method may further include determining a thickness at least one layer on the surface of the substrate. The substrate may also include a transfer layer formed on the surface of the substrate. In such a case, the method may further include etching the transfer layer after separating the template from the cured liquid. Etching the transfer layer may impart the pattern to the transfer layer.
The templates and methods described above, may for example, be used to form a semiconductor device, an optical device, a photonic device, a magnetic storage device or thin film head, a display device, etc.